The present invention relates to a zoom lens used in digital still cameras, video cameras, and the like equipped with a solid-state imaging element such as a CCD. More specifically, the present invention relates to a compact zoom lens suited for cameras and the like that have a zoom magnification of approximately 3× and that is connected to or installed in a portable information terminal or the like.
With the widespread use of digital cameras in recent years, there has been a strong demand for zoom lenses that are used in these digital cameras that provide high performance, low cost, and a compact, thin design. More specifically, in zoom lenses for cameras installed in portable telephones and the like, there is a strong demand for a zoom lens that is thin when it is retracted.
An example of a compact, thin zoom lens is a two-group zoom lens that is equipped with a first lens group and a second lens group and that allows the zoom magnification to be changed by varying the distance between these lens groups. Known examples of conventional two-group zoom lenses include: a zoom lens formed from five-six lenses with a first lens group having positive refractive power and a second lens group having negative refractive power (e.g., see Japanese Laid-Open Patent Publication Number Hei 9-166749 and Japanese Laid-Open Patent Publication Number Hei 9-211325); and a zoom lens formed from seven lenses equipped with a first lens group having negative refractive power and a second lens group having positive refractive power (e.g., see Japanese Laid-Open Patent Publication Number Hei 8-254653 and Japanese Laid-Open Patent Publication Number Hei 10-253882).
In solid-state imaging elements, microlenses are disposed on an image plane in order to make efficient use of light. Thus, if the angle of a light ray entering the solid-state imaging element, i.e., the exit angle, is too large, “shading” takes place. As a result, in lens systems used for solid-state imaging elements, it is preferable to use a telecentric optical system in which the exit pupil is positioned with a sufficient distance from the image plane, and the exit angle is small.
While the conventional two-group zoom lens with a first lens group having positive refractive power and a second lens group having negative refractive power is compact and thin and is suitable for use in silver halide film cameras, the exit angle of the outermost optical rays at the wide-angle end becomes too large, making the zoom lens difficult to use with solid-state imaging elements. Also, in the conventional two-group zoom lens with the first lens group having negative refractive power and the second lens group having positive refractive power, the exit angle can be kept small but the need to use seven lenses makes it difficult to achieve an adequately compact and thin design.